Passive and active acoustic properties of a diaphragm at low Mach number

Abstract

In this paper a low noise flow duct facility that performs a multimodal characterization of the passive and active acoustic properties of obstacles in the aero-acoustic conditions of an automotive air conditioning system is presented. The experimental procedure is made of two steps. In the first one the passive data, i.e. the multimodal scattering matrix, is measured with a multi-sources method. In the second step the outgoing modal pressure spectra radiated upstream and downstream by the flow obstacle interaction source is achieved. A numerical simulation of the experiment based on a 3D-Finite Element Method is developed. A very good agreement between the theoretical and experimental results of the no flow scattering matrix of a diaphragm is found. The effect of the flow on the scattering matrix is shown before performing the measurement of the aero-acoustic source characteristics of the diaphragm.

On the use of structured poroelastic materials for noise control at low frequency

“…()1) giving 543 Hz. Results obtained in our experimental test bench [8] are close to simulations obtained by finite element model (see [6] for more details). The model allows to analyze the dissipation mechanisms and optimize the poroelastic metamaterial according to its properties such as airgap, airflow resistivity, Young's modulus and loss factor.…”

Experimental and numerical observation of flow-acoustics feedback phenomena due to two diaphragms in tandem inserted in a rectangular duct

“…Although the detailed description of the test set up can be found in [21], it is worth recalling its main characteristics. The flow generation part is composed of a fan, mufflers, a plenum chamber and a hot wire air flow meter.…”

“…1). In the case of a single diaphragm inserted in the duct, measured scattering matrix coefficients have been validated by comparison with numerical simulations [21].…”

“…In order to obtain a formulation for both random and periodic types of signals, the sound power from values of the source vectors is obtained via the modal cross-spectrum matrix [15,22]. The formulation extracts the source strength using crossspectrum densities between the four different sections S 1 , S 4 , S 7 , S 8 according to the procedure first described in [21] and also applied in [23] (see Appendix B in [23] for all necessary details). The procedure allows us to suppress the hydrodynamic fluctuations, particularly on the downstream side where the flow is expected to be turbulent.…”